Back-Illuminated AlGaN-Based Solar-Blind Ultraviolet Photodetectors With High-Temperature Photoresponse Stability

A high thermal stability AlGaN-based back-illuminated solar-blind ultraviolet (SBUV) p-i-n photodetectors (PDs) are fabricated on double-sided, polished sapphire substrates. The PD exhibits low dark current of less than 18 pA under –5 V bias at room temperature (RT), which corresponds to a dark current density of $\lt 1.8\times 10^{-{9}}$ A/cm2. Even at a high temperature of $150~^{\circ }$ C, the dark current of the PD is still below 50 pA. The PD also shows a high solar-blind/UV rejection ratio up to four orders of magnitude in the temperature range of RT to $150~^{\circ }$ C. As the temperature continuously rises from RT to $150~^{\circ }$ C, the photocurrent of the PD only increases by less than 8%, which corresponds to an extremely small temperature coefficient (TC) of <0.06%/°C. The ultralow TC achieved is believed to be related to the high polarization electric field at the composition-graded heterojunction interface.